1. Field of the Invention
The present invention generally relates to a high-density disk structure and the manufacturing method thereof, and more particularly, a high-density disk structure that prevents the collision of an optical pickup's objective lens with a high-density disk.
2. Description of the Related Art
A compact disk (CD) is 1.2 mm in thickness and 120 mm in diameter as shown in FIG. 1. A CD has a center hole of 15 mm diameter and a clamping zone of 44 mm, which encircles the center hole. The clamping zone is an area where the CD is clamped by a damper on a spindle or a turntable installed in a disk device.
When a CD is normally placed into a disk device equipped with an optical pickup, its recording layer, which has pit patterns, is approximately 1.2 mm from an objective lens of the optical pickup. The objective lens for a CD has a numerical aperture (NA) of 0.45, which is relatively small.
A digital versatile disk (DVD) is, similar to a CD, 1.2 mm in thickness and 120 mm in diameter, as shown in FIG. 2. A DVD also has a center hole of 15 mm diameter and a clamping zone of 44 mm encircling the center hole.
When a DVD is normally placed into a disk device, its recording layer, which has pit patterns, is approximately 0.6 mm from an objective lens of an optical pickup that a disk device is equipped with. The objective lens for a DVD has a NA of 0.6, which is relatively large.
A high density-DVD (HD-DVD), which is currently being commercialized, is 1.2 mm in thickness and 120 mm in diameter and is shown in FIG. 3. A HD-DVD also has a center hole of 15 mm diameter and a clamping zone of 44 mm encircling the center hole. If a HD-DVD is normally placed into a disk device, there will be a 0.1 mm gap between its recording layer, which has pit patterns, and the objective lens of an optical pickup for a HD-DVD device. The objective lens of the optical pickup of an HD-DVD device has the largest NA of 0.85 with respect to the two other disk type devices. The optical pickup for a HD-DVD uses a laser beam of shorter wavelength than for a CD or a DVD to record or reproduce signals in high density.
Therefore, in comparison with a CD or a DVD, a HD-DVD uses an objective lens that is situated closer to the recording layer, that uses a laser beam of shorter wavelength, and that has a greater NA. According to these conditions, it is possible to concentrate a stronger intensity of light on a smaller beam spot formed on the high-density pit patterns of the recording layer of the HD-DVD. Consequently, the transmitting distance of a laser beam of shorter wavelength is shortened, and the variation of the laser beam and its spherical aberration are minimized.
Referring to FIG. 4, if a HD-DVD 10 is normally placed onto a spindle 11 of a turntable installed in a disk device, a conventional servo-controlling operation for a spindle motor 12 by a motor driving unit 13 and a servo controller 15 is conducted to rotate the placed HD-DVD 10 at a constant and high speed. While the HD-DVD 10 is rotating, a focusing-servo operation is conducted to focus a laser beam for an optical pickup 14 exactly onto the recording layer. This operation is performed by moving the objective lens OL of the optical pickup 14 in an up and down direction within an operating distance OD. If a laser beam is exactly in focus, then reproduction (or recording) of high-density pit patterns can be accomplished.
However, when the HD-DVD 10 is misplaced onto the spindle 11 by, for example, being placed upside down as shown in FIG. 5, the HD-DVD 10 will still be rotated at a constant and high speed by the combined servo-controlling operation by the turntable motor 12, the motor driving unit 13, and the servo controller 15. However, if the HD-DVD 10 has been placed upside down, the gap between the recording layer and the objective lens OL of the optical pickup 14 is 1.1 mm greater in comparison with a normally-placed HD-DVD.
In this misplacement, a laser beam cannot be focused within the conventional operating distance of the objective lens OL of the pickup 14. Therefore, the servo controller 15 supervising the focusing-servo operation continues to move the objective lens OL upward to the maximum movable distance “OD_Max” until the laser beam is correctly focused. However, in this case, the objective lens OL will collide with the misplaced HD-DVD 10. Consequently, the HD-DVD 10, the objective lens OL, and/or the servo-mechanism could be irreparably damaged.